I've built an iron golem farm in Minecraft, and I've noticed that golems don't spawn when I'm far away from it if I'm using OptiFine, even though the farm is located within the "spawn chunk" area that should always be loaded. If I switch to vanilla Minecraft without OptiFine, the farm works properly even when I'm far away. It also works under OptiFine when I'm near the farm.
I'm running Minecraft 1.8.4 with the official Mojang launcher, and OptiFine 1.8.4 HD D4 Ultra. No other mods. The farm is basically right next to the world spawn point; the whole thing is within about 40 blocks of it. I'm traveling to a distance of about 600 blocks for testing "far away". I'm staying entirely in the overworld, so the Nether isn't involved.
With vanilla, my farm produced about 40 iron in about half an hour while I stood at a distance of roughly 600 blocks. With OptiFine loaded, it produced zero iron in an entire hour of idling at the same distance. Items dropped on the ground did disappear, though, so it seems that the farm's chunks are still loaded at least to some extent under OptiFine.
Is there a way I can fix this? I want to use OptiFine for its connected textures and anisotropic filtering, but I also want my iron farm to work. As a guess, I tried turning off OptiFine's "lazy chunk loading" setting, since the tooltip says that turning it off gives you "default server chunk loading", but it didn't make a difference.